This invention relates generally to methods and apparatus for energy conservation in pressurized fluid systems and, more particularly, to methods and apparatus for controlling leaks in pressurized fluid systems such, for example, as pneumatic systems, to thereby conserve energy in such systems.
Although the invention will be described as applied to a pneumatic or compressed air system, those skilled in the art will readily understand that the invention is equally applicable to other types of pressurized fluid systems, e.g., hydraulic systems which provide motive force for any type of fluid-driven equipment and systems for industrial, process and medical applications which utilize compressed gases such as argon, helium, nitrogen and the like.
Compressed air provides the motive power for tools and machinery in a great number of industrial and other applications. For example, compressed air is used to power various types of tools such, for example, as grinders, screwdrivers, impact wrenches, nut runners, hoists and saws, among others.
In a typical factory equipped with compressed air systems, air-driven tools at work stations throughout the plant are fluidly connected to a network of pipes by long, flexible hoses or drops. Thus, in certain instances a plurality of air tools at a corresponding plurality of work stations are interfaced with the pipe system through multiple drops. The system generally must present the air tool in a manner so as to allow the operator a relatively wide range of flexibility or freedom of movement in his work and, moreover, provide the compressed air in a manner such that it is suitable for use in air tool motors and equipment.
A significant problem exists in conventional compressed air systems, namely, the leakage of compressed air from various leakage points present in the air drops. Although at first blush the problem may not appear significant, it will be seen from the following that in fact the costs resulting from air leakage are surprisingly high.
A typical air drop for an air tool in a conventional compressed air system generally employs a flexible hose, various couplings, quick disconnects and filter-regulator-lubricator (FRL) units. Points of potential air leakage associated with air drops in common compressed air systems include the connections of the air drop to the main header or overhead pipe network, various hose connections including the quick disconnects, hose deterioration, tool control valves, the filter-regulator-lubricator units, machine connections and the machine air components themselves, such as valves, piston, nozzles, etc. Indeed, a single typical air drop may have a total of six to ten potential leakage points.
Moreover, even though air demands of any single tool are generally intermittent, i.e., the tool at the end of each air drop is usually operated on an intermittent basis, conventional systems are typically constructed so that each air drop is at all times at the full or line pressure which exists in the pipe network. It is not uncommon in some facilities for each air drop to "seek" line pressure for times on the order of about 6000 hours per year. When it is considered that the tool is used approximately 20% of the time, it is seen that the air drops are subject to leakage loss about 80% of the time that the compressor is in operation.
Although the area of a single leakage point in an air drop may be relatively minute, e.g., 0.0005 in.sup.2, six such leakage points in a single air drop have a cumulative effective leakage area of 0.0030 in.sup.2 which is equivalent to a leakage opening having a diameter of 1/16 inch. This corresponds to a leakage rate of about 6.49 cfm at 100 psig line pressure. With the cost of generating compressed air presently being on the order of 28 cents per 1000 cubic feet, the losses incurred at a single air drop having leakage points as described above amounts to about $607.00 per year. It has been estimated that there are about 7,000,000 air drops presently in existence through which air tools and equipment are connected to air supplies. When viewed in this light, it is seen that the costs of air leakage are in fact quite significant.
Presently, air leak control is a rather haphazard operation involving detection essentially through observation or through maintenance procedures. Currently available products are generally limited to instruments that can only identify leakage points for manual repair and the costs of maintenance crews for spotting and correcting leaks is enormous. Indeed, many leaks are never found due to the difficulty of detecting a tasteless, odorless and colorless gas which leaks with a noise which is generally inaudible over plant background noise.
In order to compensate for air leakage, compressors are often oversized by 15 to 20% with consequent increased energy costs thereby further increasing the high cost of leakage maintenance.